Signal processing, regardless of the precise type of signal (e.g., radio frequency (RF) or photonic), requires some means for combining, or adding, multiple signals or inputs into a single output. With respect to high-speed photonic signal processing, single-mode fibers or waveguides may be used and are highly preferred; however, coherent interference results in unstable (noisy) output. While partial solutions are possible, each has particular drawbacks. For example, it may be possible to detect a plurality of single-mode optical inputs with a high-speed photodiode, but this results in an RF-domain output signal (which in turn requires noisy RF amplifiers that may introduce distortion) and will not scale to a large number of inputs. Alternatively, photonic inputs may be combined via a single-mode to multi-mode (SM/MM) combiner (SMC) and detected via commercial off the shelf (COTS) high speed detector designed for multimode optical fiber, but this approach similarly results in an output in the RF domain, rather than the single-mode optical domain.